This invention deals generally with subsurface structures for detention, retention and ground infiltration of stormwater runoff, and more specifically with a modular concrete structure composed of two or more side by side vault shaped chambers.
Many laws and regulations exist that require the slow release of stormwater into the aquifer, while the somewhat conflicting requirement for traffic safety is for quick drainage of water from roadways. Laws and regulations also exist that require the slow release of stormwater to open water ways and the aquifer and the recharge of the aquifer with all the water from small storms. Although this problem was once addressed by merely constructing drainage basins a short distance from roadways, the value of land, particularly in urban and suburban areas, makes surface drainage basins impractical. One solution to this problem is to put stormwater retention and infiltration structures underground. For road construction, such structures can even be installed directly below the roadway.
A common structure used for this purpose is an arch shaped corrugated molded plastic chamber. Such structures are disclosed in U.S. Pat. Nos. 5,890,838 to Moore, Jr. et al; 6,612,777 to Maestro; and 6,854,925 to DiTullio. However, the cost of such molded plastic structures is significant because the cost must cover the expensive mold. Another commonly use solution is the installation of concrete pipe or metal pipe. The installation of these structures is labor intensive because they are multiple single components, each of limited volume. The structures must provide a structurally stable foundation, which involves serious compaction requirements of the backfill that also is very labor intensive and impractical due to the shape of the structures and their placement relative to each other. The plastic structures suffer from material weaknesses that compromise the structural stability because plastic is subject to relaxation and creep of the material that are in excess of what is acceptable, and this has led to subsidence of the grade levels above the structures. The metal structures corrode and have a relatively short live span compared to un-reinforced concrete. Moreover, there is little ability to customize any such structure except for cutting shorter segments off the standard product.
It would be very beneficial to have available a shallow subsurface detention or retention and infiltration structure to accommodate to the surface area that needs drainage, to the quantity of stormwater runoff to which the surface is subjected, that can be installed with common construction equipment such as front-end loaders, backhoes, or small cranes, and which also covers substantially more area with one placement than can be covered with the single pipe or arched sections used until now. Furthermore, it would be very beneficial to be able to place backfill on top of the structure to become the work surface for setting the next section. It also would be beneficial to have available a subsurface retention and infiltration structure that can easily be customized to accommodate to the width and the length of a surface that needs drainage and to the quantity of stormwater runoff to which the surface or roadway is subjected. It would be even more desirable if such structures could be constructed and installed at costs less than the previously described systems.